As we begin a new year, it’s worth reflecting on the paradoxical and frustrating nature of progress. Progress is often disappointing, because even when it indisputably occurs (as it often does), it spawns new problems or reveals that old problems were underestimated in their complexity or inertia.

Gains are forgotten and taken for granted. They become part of society’s norms, no longer celebrated because their existence is assumed to be permanent. Meanwhile, younger generations focus attention and discontent on new disputes and conflicts, as if the earlier advances had never occurred.

Progress resembles a parabola: first, spurting ahead; then, slipping back. In 2017, the uproar over sexual harassment exemplified this cycle. A root cause, of course, was the massive entry of women, beginning in the 1960s and 1970s, into the paid labor market.

Then as now, this was widely regarded as a major advance in social progress, because it afforded women more personal choices. But there was a perverse, messy and unfortunate side effect: With more women in the workforce, there was more sexual harassment; men had more opportunities to exploit positions of power. In 1960, women represented less than a third of all workers; by 2010, they were nearly half.

Or take the shooting of young black men by police. Compared with the 1960s, most urban police forces are now far more integrated. In 2013, according to Justice Department statistics, racial and ethnic minorities — mostly African Americans and Hispanics — constituted 27 percent of local police officers, up from 15 percent in 1987.

These are clear advances, but they haven’t fully repaired the strained relations between many local police forces and the communities they patrol. The task of controlling crime and forging constructive connections with urban neighborhoods is tougher than just integrating the police.

A final example: the Internet. In its early years, it was lauded as a technological marvel that would propel us into a brave new era of democratic openness, intellectual collaboration and economic efficiency. With time, the promise has faded or, at the least, become more qualified, as the Internet has evolved into a vehicle for many not-so-wonderful activities: invasions of privacy; cyberbullying by adolescents and others; the hacking of business, governmental and personal computers (including the interfering with the 2016 U.S. election); the creation of “fake news”; identity theft; and the theft of trade secrets.

None of this should be taken as an argument to do nothing about the nation’s social ills, just because the reality is likely to prove more complicated and less malleable than the rhetoric of “reform” suggests. We obviously should not (and won’t) remove women from the workforce; or re-segregate local police forces; or dismantle the Internet.

The more modest goal here is to keep things in perspective — to remember constructive change when it occurs and to recognize that some of our goals are utopian. We need to match our expectations with practicalities. One of the reasons for our disillusion with politics, though certainly not the only one, is that we set out unrealistic objectives and then feel betrayed when we discover they’re unobtainable.